1. Field of the Invention
The present invention relates to a transfer apparatus and an image forming apparatus.
2. Description of the Related Art
A conventional image forming apparatus incorporates a transfer roller that transfers a toner image from a photoconductive drum onto a medium such paper. If the transfer roller has a hard surface, the toner image is not transferred normally, resulting in uneven transfer of the toner image. A transfer apparatus has been proposed which uses a transfer roller having a surface formed of a foamed material. Thus, a transfer roller with less hardness can be obtained.
Foamed cells exposing on the surface as in the conventional transfer apparatus exhibit poor endurance performance. In other words, as the cumulated number of printed pages increases, the resistance of the transfer roller increases, and therefore the voltage dependency of the resistance increases. This makes it difficult to control transfer current, and causes poor image quality.